In manufacturing and assembly processes, it is often desirable to analyze an object surface to determine the nature of features and/or irregularities. The displacement (or “profile”) of the object surface can be determined using a machine vision system (also termed herein “vision system”) in the form of a laser displacement sensor (also termed a laser beam “profiler”). A laser displacement sensor captures and determines the (three dimensional) profile of a scanned object surface using a planar curtain or “fan” of a laser beam. In a conventional arrangement, a vision system camera assembly is oriented to view the plane of the beam from outside the plane. This arrangement captures the profile of the projected line (e.g. extending along the physical x-axis) on the object surface, which, due to the baseline (i.e. the relative spacing along the y-axis) between the beam plane and the camera causes the imaged line to appear as varying in the image y axis direction as a function of the physical z-axis height of the imaged point (along the image x axis). This deviation represents the profile of the surface in the x-z plane, which is derived from the x-y position of individual image points using appropriate calibration parameters within the displacement sensor. Laser displacement sensors are useful in a wide range of inspection and manufacturing operations where the user desires to measure and characterize surface details of a scanned object via triangulation. A typical laser displacement sensor uses a vision system camera having a lens assembly and image sensor (or “imager”) that can be based upon a CCD or CMOS design. The imager defines a predetermined field of grayscale or color-sensing pixels on an image plane that receives focused light from an imaged scene through a lens/optics.
In certain vision system implementations, a plurality of displacement sensors (e.g. laser profilers) are mounted together to extend the overall field of view (FOV) (wherein the term “field of view” refers to measurement range) of the vision system so as to fully image a desired area of the object (e.g. its full width) with sufficient resolution.
It can be challenging to read a projected line on the surface of an object of interest that is made of materials with different optical properties and/or has a structured surface that can cause internal reflection. For example, surfaces can include opaque regions, specular regions, translucent/transparent regions or a combination of such, which reflect differently, and depending upon their relative angles, can also produce internal reflections. The former case is challenging because choosing a single exposure setting to accommodate all materials is problematic, while the latter case is challenging because the internal reflection can confuse the displacement sensor as to the actual profile.